1. Field of Invention
The present invention relates to a golf club, particularly to its structure for securing a balance weight thereto.
2. Prior Art
It is a known art to provide a golf club head with a balance weight secured to a sole. FIG. 4 through FIG. 6 illustrate one example of such conventional golf club head 1, which is a long iron club in this example. The head 1 is hollow and metallic, having a face 2 at its front side, a back 3 at its back side, a sole 4 at its lower side, a top 5 at its upper side, a heel 6 at its proximal side and a toe 7 at its distal side, respectively. The heel 6 is formed with a neck 8, from which extends upwardly a hosel 9. The hosel 9 serves as a shaft connector for connecting a shaft 10 thereto. Incidentally, a plurality of nearly horizontal concave grooves 11, which are called score lines, are formed on said face 2.
The head body 16 forming the majority portion of said head 1 is constructed by for example joining a plurality of metallic plate members together by welding or the like, said metallic plate members being forged for example, so that it is made hollow thereinside. A plurality of metallic balance weights 17 are fixed securely to the outer surface of the sole 4 of the head body 16, projecting downward therefrom. While the material of said head body 16 is either iron-based or titanium-based, the material of each balance weight 17 is beryllium copper for example, so that the specific gravity of the latter is larger than that of the former.
In other words, one of the objects of the balance weight 17 is to lower the center of gravity of the whole head 1. With the center of gravity thus lowered, balls are made easier to raise when they are struck, thus resulting in elongated travelling distances thereof. On the other hand, each balance weight 17 is formed slender, elongated in the back-to-front direction, having beveled portions 18 on its lower face on all sides, and thus, it is another object of the balance weight 17 to reduce a contacting area with the ground at the time of striking balls so as to lessen the resistance of the head 1 against the ground.
Whereas, there is illustrated in FIG. 6 a conventional method of fixing the balance weight 17 to the head body 16. According to the conventional method, a through-hole 21 is defined through an outer shell corresponding to the sole 4 of the head body 16, into which is inserted a projection 22 formed on an upper face of the balance weight 17, as illustrated in FIG. 6A. Thereafter, the projection 22 is caulked using a press device or the like in order to form a caulked portion 23, thereby fixing the balance weight 17 to the head body 16, as illustrated in FIG. 6B. It is to be noted that the caulked portion 23 is located inside the head 1, when the head 1 is finished. Incidentally, reference numeral 24 indicated in FIGS. 6A and 6B designates a weight plate provided on an inner face of the outer shell, corresponding to the sole 4 of the head body 16.
According to the conventional fixing method using caulking, however, there are limitations to the materials which can be used for the balance weight 17. Materials with less extensibility are unsuitable for caulking. Taking tungsten for example, it has insufficient extensibility, and unsuitable for caulking, although it is suitable as a material for a balance weight due to its relatively large specific gravity.